Barack Obama took his place in history tonight when the Democratic convention formally adopted him as their presidential nominee, the first African American to lead a major political party into election.

Tonight's vote had been suspenseful, with the Obama camp concerned until the last moments it could emerge as a potential flashpoint for hardcore supporters of Hillary Clinton.

Instead, it became a raucous celebration of Obama's candidacy, punctuated by chanting of his campaign slogan, "yes, we can".

In a carefully crafted piece of political theatre, Clinton emerged on the convention floor midway through the roll call vote to urge Democrats to embrace Obama as their nominee.

"Let's declare together in one voice right here, right now that Barack Obama will be our presidential nominee," she said.

Clinton went on to call for a suspension of the vote and for Obama to be adopted by acclamation. Moments later, a roar went up from the convention floor and it was done.

Tonight's events could at last bring closure to the Democrats' long and bitter primary campaign.

The scene for the closing of ranks around Obama was set in motion earlier today when Clinton formally released her delegates, freeing them to vote for Obama.

"You've come here from so many different places having made this journey and feeling in your heart what is right for you to do," she told the crowd in emotional scenes.

"I want you to know that this has been a joy. Yes, we didn't make it. But, boy, did we have a good time."

She did not go so far as to direct her followers how to vote, but as the traditional roll call of the states got under way, beginning with Alabama, it soon became apparent that most Democrats wanted to set the past aside, and focus on Obama's election battle against John McCain.

Clinton's name was placed in nomination by the farm workers' leader, Dolores Huerta. Obama was nominated by an Iraq war veteran from Tennessee.

Some Clinton supporters did register their support for their candidate, but it was clear within the opening minutes of the vote, but by far the greater majority had swung around behind Obama.

Even Arkansas, which Clinton claims as her adopted state, rallied behind Obama, in a unanimous vote for his candidacy that drew huge whoops from the crowd.

Obama also handily carried Kentucky, a state that had voted by huge margins for Clinton in what as then seen as a sign of his difficulty in appealing to white working-class voters.

Tonight's nomination vote had been one of the most contentious issues between the Obama and Clinton camps.

At first, the Obama camp had been uncertain about holding a vote at all. But the Clinton camp applied relentless pressure.

Clinton argued that her disappointed supporters needed to be allowed to cast their votes for her as a form of "catharsis", and a number of activists started petition campaigns calling for a vote.